In the operation of steel wheeled transit vehicles in light rail or heavy rail systems, the wear of wheels with time can significantly affect the accuracy and efficiency with which vehicle operation can be controlled.
Thus, in comparing the speeds of axles for spin/slide control, compensation is required for any difference in the sizes of the wheels. Further, since the ratio of axle speed to vehicle speed changes as wheel size changes, it is preferred that the axle speeds be adjusted so that the axle speeds indicate the vehicle speed.
Wheel size changes also relate to tractive effort control. As wheel size decreases, less tractive effort is required to achieve a particular acceleration rate. Tractive effort adjustment for wheel size changes allows tight tolerances on acceleration and deceleration rates regardless of wheel size. By eliminating excessive tractive effort through control adjustment the frequency of spins and slides is reduced as the wheels wear.
In the prior art, one typical approach employed to address the wheel wear problem involves the automated sampling of car axle speeds under vehicle coasting conditions and automatically computing wheel wear compensation factors relating each axle speed to the speed of a preselected axle speed. The compensation factors are then employed in velocity difference calculations used to detect spins of slides.
The value of this prior art approach to wheel wear compensation is limited by the fact that it only compensates for relative wheel wear between axles because it employs the speed of one axle as a floating reference. Thus, relative wheel wear compensation is useful only in velocity difference calculations in spin-slide control and has no utility in making tractive effort compensation in normal power or braking control. Further, relative wheel wear compensation has no utility in the conversion of rotational speed to linear speed in linear speed monitoring and control.
In the prior art, absolute wheel wear compensation has been achieved for tractive effort compensation and linear speed monitoring and control by periodically measuring actual individual wheel sizes and entering the individual wheel sizes into each controller included in the vehicular control system. This procedure is time consuming and it is error prone because each wheel size must be entered in correspondence to the speed input for its axle.
Accordingly there has been a continuing need for highly automated, absolute wheel wear compensation so as to achieve improved accuracy and efficiency in vehicle operation.